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Biology: Mitosis and Meiosis Cheat Sheet by

What is DNA?

DNA- deoxyr­ibo­nucleic acid, the hereditary material of life in a cell's nucleus
genes- carries codes for traits
trait- charac­ter­istic of an organism
acquired trait- from your parents
envi­ron­mental trait- from the surrou­nding enviro­nment
chromosomes contain genes which are made of DNA
Genes are inherited from your parents. Each gene codes for 1 trait, and thousands of genes are on each chromo­some. Chromo­somes in humans are arranged into 23 homo­logous pairs

DNA Structure

DNA is a double helix, and consists of phos­pha­te, deox­yribose sugar, and nitrogen bases. Phosphate and sugar make the backbone, and nitrogen bases are the rungs of the ladder.
nucl­eot­ide- a phosphate paired with a nitrogen base and deoxyr­ibose sugar
hist­one- special proteins that prevent DNA from tangling
nucl­eos­ome- DNA and histone packages which resemble beads
telo­mere- protective end on eukaryotic cells that shortens every time DNA replicates

The 4 Nitrogen Bases

Adenine to
Th­ymine with 2 H-bonds
Guanine to
Cy­tosine with 3 H-bonds

What Causes Genetic Diversity?

1. Crossing over in prophase I
2. Indepe­ndent assortment in meta­phase I and II. The chromo­somes line up randomly each time.


non-­dis­jun­cti­on- a mistake that occurs during anaphase I and II, when the chromo­somes do not separate and gametes end up having the wrong number

Mitosis vs Meiosis

- all daughter cells are somatic
- both for the purpose of reprod­uction
- all daughter cells are gametes
- 2 similar cells are produced
- both create daughter cells
- 4 different cells are produced
- 46 chromo­somes
- 23 chromo­somes
- DNA is not crossed over
- DNA is crossed over

Meiosis I and Meiosis II

Prophase I
centrioles move to opposite poles, homologous chromo­somes become visible and form tetr­ads, crossing over occurs, genetic material is exchanged
Prophase II
- centrioles move to opposite poles, chromosome pairs become visible, crossing over does NOT occur
Metaphase I
- tetrads line up along the equator of the cell (staying as a pair)
Metaphase II
- each chromosome moves to the equator of the cell
Anaphase I
- homologous chromo­somes are pulled apart creating whole paired chromo­somes on each side
Anaphase II
- each chromosome splits and moves to opposite poles, the chro­matid is now considered the chromosome
Telophase I
- nuclear membrane reforms, cytoki­nesis occurs, creating 2 diploid cells, which contain 46 chromo­somes and are geneti­cally different
Telophase II
- nuclear membrane reforms, cytoki­nesis occurs, creating 4 haploid cells called game­tes

Prokar­yotes vs Eukaryotes

- no nucleus or organelles
- both forms of life
- nucleus and organelles
- simple and primitive
- complex cells
- usually single­-celled
- can be multic­ellular

Meiosis Defini­tions

zygo­te- cell created when egg and sperm unite
kary­oty­pe- map of chromo­somes organized into homologous pairs
dipl­oid- total # of chromo­somes in an organism, somatic cells
hapl­oid- half the # of chromo­somes in an organism, sex cells

Purpose of Mitosis and Meiosis

1. Asexual Reprod­uction
- 1 parent with identical offspring
1. Create Gametes
- creates egg/sperm or egg/pollen
- 2 parents with geneti­cally different offspring
2. Repair
- to fix damaged cells and replace old cells
3. Growth
- nuclear division, and depends
on the size and growth of the


muta­tion- any change made to DNA

4 Types of Mutations

1. Tran­slo­cat­ion
- part of a chromosome breaks off and attaches itself to a different chromosome
- Transl­ocation Down's
2. Dele­tion
- part of a chromosome is deleted
- Prader Willi Syndromelearning disabi­lities, behavi­oural problems, obesity, short stature, etc.
3. Dupl­ica­tion
- part of the chromosome is repeated
- cause of seizures
4. Inve­rsion
- genetic code is flipped
- linked to infert­ility problems

Trisomies and Traits

Trisomy 13, Patau Syndrome
heart defects, brain and spinal cord abnorm­ali­ties, extra fingers and toes, cleft lip, usu. die by 1 yr. old
Trisomy 18, Edward Syndrome
abnormally shaped head, clenched fists, heart defects, usu. die by 1 yr. old
Trisomy 21, Down Syndrome
mild disabi­lity, can still form relati­onships and interact in society
Trisomy XXY, Klinef­elter Syndrome
infertile males, look childish, high pitched voice, learning disabi­lities

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